In the field of liquid crystal display devices, it is a future trend to slim the bezel of the liquid crystal display device. Therefore, in the fabricating process of a backlight module of the liquid crystal display device, it is very important how to expand a view area of the backlight module and reduce a bezel of the backlight module. In an edge-illumination type backlight unit, the light guide plate is a very important optical member. The type of positioning for light guide plates can affect the bezel thickness of the liquid crystal display device. In general, a positioning column is used for fixing light guide plates, wherein the positioning column is fixed in the backplate of the backlight module by many fabricating methods, and a press riveting method is the most common one.
In the press riveting process, a riveting die is fixed on the punching machine, and a hole is form in a metal sheet. The metal sheet is disposed on a female mold with draw holes, the hole on the metal sheet is corresponding to an inner hole of the female mold, and the diameter of the hole on the sheet metal is identical to the diameter of the inner hole of female mold. Then, the positioning column to be press riveted is disposed in the hole of the sheet metal. Finally, the positioning column is riveted in the metal sheet by punching. After finishing the press riveting process, the metal sheet is taken off from the mold.
Referring to FIGS. 1 and 2, FIG. 1 illustrates a structure view according to a conventional backplate assembly 1. FIG. 2 illustrates a cross-sectional and enlarged view of a positioning column 12 of the conventional backplate assembly 1 along line A-A of FIG. 1.
A backplate assembly 1 is used to accommodate and position an optical unit 2. The backplate assembly 1 comprises a backplate 10, a plurality of step-shaped holes 11, and a plurality of positioning column 12.
The backplate 10 has a plate 101 and a vertical lateral side 102. The plate 101 has a first surface 1011 and a second surface 1012. The vertical lateral side 102 vertically surrounds the plate 101. The step-shaped holes 11 are formed in the backplate 10, and the step-shaped hole 11 has a first opening 111, a second opening 112, and a ring step concave part 113. The first opening 111 is formed in the first surface 1011, the second opening 112 is formed in the second surface 1012. The ring step concave part 113 is formed between the first opening 111 and the second opening 112, and the first opening 111 is smaller than the second opening 112.
Each positioning column 12 has a column body part 121 and a ring-shaped shoulder part 122. The column body part 121 has a positioning function for positioning an optical unit 2, wherein the optical unit 2 has a plurality of positioning parts 21 corresponding to each column body part 121. Each ring-shaped shoulder part 122 is formed on an end of each column body part 121. Firstly, each column body part 121 of the positioning column 12 penetrates into the second opening 112, and passes through the corresponded first opening 111.
Then, each positioning column 12 is riveted into the plate 101 by punching, wherein the ring-shaped shoulder part 122 of each positioning column 12 and the ring step concave part 113 of the step-shaped hole 11 are closely combined to each other, such that each positioning column 12 is fixed in the backplate 10. The diameter of the column body part 121 of each positioning column is referred to as D1, and the diameter of the ring-shaped shoulder part 122 of each positioning column 12 is referred to as D2.
During a fabricating process of the backplate assembly 1, each positioning column 12 is riveted into the plate 101 by press riveting, and then a part of plate 101 is bent to form the vertical lateral side 102. If the second opening 112 is too close to or beyond the bending area of the plate 101, the second opening 112 and the ring-shaped shoulder part 122 of the positioning column 12 are deformed due to the bending movement for forming the vertical lateral side 102. Therefore, if it is anticipated that the column body part 121 of the positioning column 12 can be very close to the vertical lateral side 102; that is, if a distance L1 between the column body part 121 and the vertical lateral side 102 is approaching zero, the diameter D2 of the ring-shaped shoulder part 122 should be smaller than or equal to the diameter D1 of the column body part 121, such that the second opening 112 can't contact with the bending area of the plate 101 for forming the vertical lateral side 102.
The bezel thickness of liquid crystal display device is determined by a distance between the largest view area and the vertical lateral side 102, and the largest view area of the optical unit 2 is limited to the distance between the column body part 121 of each positioning column 12 and the vertical lateral side 102. When the distance L1 between the column body part 121 and the vertical lateral side 102 can't be reduced, the largest view area of the optical unit 2 is unable to be enlarged, such that the bezel thickness of the liquid crystal display device can't be reduced.